Optical system for sound reproduction



p 1937- H. J. HASBROUCK, JR 2,093,012

OPTICAL SYSTEM FOR SOUND REPRODUCTION Filed July 24, 1935 ;(\:IIIIIIIIIIIIIIIIIIIII IIIIIIIIII I) INVENTQOR Harold J. Hasbrnuck, J1".

ATTORNEY Patented Sept. 14, 1937 OPTICAL SYSTEM FOR SOUND REPRODUCTION Harold J. Hasbrouck, Jr., Flushing,

N. Y., assignor to United Research Corporation, Long Island City, N. Y., a corpcration of Delaware Application July 24, 1935, Serial No. 32,862

7 Claims.

This invention relates to the reproduction of sound and particularly to the reproduction of sound from diapositive records wherein a light sensitive device is utilized for translating light variations into corresponding electrical variations.

An object of the invention is to increase the efiiciency of translation of light modulations into electrical currents.

device.

A further object of the invention is to eliminate moving shadows over a light having non-uniform response In the art of sound sensitive material characteristics.

reproduction from linear carriers such as talking motion picture film, a

constant light source defined by a slit on to the emergent light being impre tive material in accordance transmission through projects a beam of light a sound record of a film,

ssed on light sensiwith the varying the sound record. In the case of a variable area record, that is, one in which the opaque portion varies in width in accordance with sound, shadows move back and forth over the light sensitiv cordance with the opaque ou track. Since it is not possible e material in actline 0f the sound to obtain a photosensitive surface perfectly uniform over its entire area, the electrical energy output of the device will not exactly correspond to the light variations.

Although this is true of any photosensitive device whether a photo-electric cell or the varying larly true in resistance type of cell, it is particuthe case of a selenium cell wherein a large number of fine electrodes are interdigitated to form the light sensitive surface. As the shadows pass over the surface there may be a slight variation in resistance section of the electrodes, with stead of a the movement of the light, a may be obtained in the output of each alternate the result that insmooth variation in accordance with stepped variation of the cell.

The present invention eliminates any deleterious effects caused by these variationsin resistance or response, by changing the light modulations as impressed on the cell from those of variable area to those of variable intensity.

The cell is thus completely illuminated in accordance with the amount or quanta of light passing through the sound track portion of that all units of the cell add th the film with the result eir response simultaneously to produce an over-all effect not subject to the total response of a ny particular unit.

The invention contemplates, therefore, a rectangular light source imaged in an objective lens which in turn images a rectangular slit upon the sound track portion of a film. A cylindrical lens on the opposite side of the film unidimensionally 5 images the objective lens, in which the light source image lies, upon the light sensitive surface of a light sensitive cell, such as selenium. As this surface is substantially square and the beam of illumination passing through the film is rectangular, the cylindrical lens functions to reduce the beam to the desired dimensions.

The details of the invention will be more fully understood by reference to the following description read in conjunction with the accompanying drawing, in which Fig. 1 is a cross-sectional view of the essential elements of the invention.

Fig. 2 is a perspective diagrammatic view of the elements of Fig. 1.

Figs. 3 and 4 are detail views of one type of photo-sensitive device which may be used in Figs. 1 and 2; and

Fig. 5 is a detail view of the section of the holder employed for an optical element and a photo-sensitive device such as a selenium cell.

Referring now to Fig. 1, a lamp 4 of constant intensity projects light from a rectangular filament 5 through an optical assembly 6 having a condenser lens 8, a slit mask 9, cup-shaped mem- 3O bers It] for stifiening the assembly, and an objective lens ll. Emergent light from the assembly 6 is projected on the sound track portion of a film l2 positioned by a shoe l 3 having an aperture [4 therein through which the light passes to a cylindrical lens l6 and a photo-sensitive device in the form of a selenium cell l'l.

Referring to Fig. 2, the essential elements of Fig. 1 are arranged in perspective to aid in explaining their relationship, the film [2 being 40 shown as having a variable area sound track 20 and the selenium cell I! as having a light sensi tive portion 2|. Cell I1 is shown connected through an amplifier 23 to a sound reproducer 24.

In the operation of the above system, the light from the filament 5 passes through the condenser lens 8, the slit of the mask 9 through the objective lens H, the sound track 20, lens it, on to the light sensitive surface 2l of the cell !1. The filament 5 is imaged in the objective lens ll 50 while the objective lens H images the slit 9 upon the sound track 20. In usual practice the cylindrical lens i6 is not used and the selenium cell l! is positioned close to the film, the light sensitive surface 2| thus receiving moving shadows or light according to the outline of the sound track 26 passing the aperture M of the shoe l3. Fig. 3 illustrates this condition by showing a shadow or light spot 26 which represents a unit length of sound track determined by the slot in mask 9. The dotted lines 2i and 28 represent different positions of the shadow 26 caused by different units of the sound track at the aperture Hi. It is thus realized that as the shadow 26 passes back and forth over the light sensitive surface 2! dififerent amounts of the surface starting from the left hand side of the cell in Fig. 3 will be darkened and illuminated with the result that unless the variations in resistance of each selenium strip making up the cell are equal to another for equal light intensities, the output of the cell will not be increased and decreased uniformly and smoothly as the shadows pass thereover but in non-uniform steps. I

Returning now to Figs. 1 and 2, the selenium cell ll is shown positioned back from the film with the cylindrical lens is interposed therebetween so as to image the objective lens ii and the filament appearing therein on the sensitive surface 2i in one direction only. Since the filament image appearing in the objective lens H is rectangular, it is only necessary to reduce the rectangular section in one direction to completely fill the light sensitive area with the light as seen at the objective lens H. In this manner the sound track functions as a variable stop or iris and varies the intensity of the light over the entire cell in accordance with thevariations in opacity on the sound track portion which varies the quanta of light passing therethrough.

In Fig. l the area or beam of illumination on the cell is shown by the dotted lines 3i when the cylindrical lens is not used, the cylindrical lens compressing this rectangle into substantially a square just covering the interdigitations constituting the sensitive area of the cell. Being completely illuminated, each individual section or unit of the cell will vary with the total illumination thereon, the final output of the cell thus being the additive or cumulative reaction or response of each unit which will provide a uniform over-all effect.

In Fig. 5 a portion of the holder for supporting the cell ll and the cylindrical lens it in proper fixed relationship is shown as a section of insulating material 32 having an opening in which is positioned the cell ii, the front portion of which is maintained against the front wall of the opening by contact springs ill to which are connected the outgoing terminals. The cylindrical lens 56 is positioned in the front portion 3'5 and may be sealed therein, the front wall having an opening in line with the light sensitive surface of the cell ll. This holder is disclosed and claimed in U. S. Patent No. 2,031,646 of Feb. 25, 1936.

It is to be understood that this invention is applicable to other photo-sensitive devices such as electrolytic or photoelectric cells of the caesium or potassium type wherein it is desired to vary the intensity over the entire cell in preference to permitting modulations to impinge thereon as moving shadows over their light sensitive surfaces.

What is claimed is:

1. An apparatus for producing sound from a sound record on a film, comprising a light sensitive cell having an electrode of definite dimensions and shape, an objective lens for projecting an image of an illuminated slit onto the sound record on the film, said electrode being positioned to receive light rays which pass through portions of the sound record, a collective lens positioned between said objective lens and said cell, and a source of light rays having a definite size and shape, said objective lens and said collective lens having such a shape and position with respect to the size and shape of said light source and the size and shape of said light sensitive cell that the image of said light source corresponds to the light sensitive portion of said electrode.

2. An apparatus in accordance with claim 1 in which said collective lens is a cylindrical lens modifying the image of said light source in one direction only.

3. A system of sound reproducing from a sound record on a film comprising a selenium cell having an active surface approximately square in shape, an objective lens for projecting an image of an illuminated slit onto the sound record of said film, said active surface of said selenium cell being positioned to receive light rays which pass through portions of the sound record, a light source having a rectangular light emitting portion, and a collective lens positioned between said objective lens and said cell and having a shape such as to distort the image of said light emitting portion of said light source to a size comparable to the size of the active surface of said selenium cell.

4. In a sound recording system the combination of a light source having a rectangular light emitting portion, a light defining slit, a film having a sound track portion thereon, a lens intermediate said'slit and said film for projecting an image of said slit on the sound track portion of said film, a lens for imaging said light emitting portion of said light source in said objective lens, a light sensitive device having a light sensitive surface of different size and shape than the light emitting portion of said light source, and a lens intermediate said film and said light sensitive device for re-imaging the light emitting portion of said light source on the lightsensitive portion of said light sensitive cell with a size and shape comparable to the size and shape of the light sensitive portion of the light sensitive cell.

5. A sound reproducing system in' accordance with claim 4; in which said last mentioned lens comprises a cylindrical lens varying the image of said light source in one direction only.

6. The method of obtaining variable intensity actuation of a light sensitive cell by a variable area sound record from a light source having a different size and shape than the size and shape of the light sensitive portion of said cell comprising imaging the light source at a point intermediate the light source and sound track and re-imaging the light source upon the light sensitive surface while distorting the image to the size and shape of thelight sensitive portion of the light sensitive cell.

'7. The method of actuating a light sensitive surface with variable density light variations with a variable area sound record, said light being generated by a linear light source of different size and shape from that of said light sensitive surface comprising translating said linear light source into a light beam of rectangular cross section corresponding in size and shape to the size and shape of said light sensitive surface and varying the intensity of said light beam without varying the size thereof by transversing a variable area sound record thereacross.

HAROLD J. l-IASBROUCK, JR. 

